1. Field of the Invention
The present invention relates generally to labyrinth seal, and more specifically to a process for designing a labyrinth seal in which flutter in the lab seal is minimized.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
Knife-edge seals, also known as Labyrinth seals or lab seals are commonly used in turbo-machinery applications such as a gas turbine engine. Lab seals are used in annular cavities between rotating and stationary components to control leakage flow rates between high pressure and low pressure cavities. The flow through the lab seal is a function of the geometry and pump (or engine) flow parameters at the inlet and discharge ends. The geometry parameters include the following: the number of knife-edges; the knife-edges axial spacing; the knife-edge radius from the rotating centerline; the volume of the cavities formed between adjacent knife-edges; and the radial clearances between the knife-edges and the seal land.
The pump or engine parameters that effect seal leakage are the seal clearances, the fluid temperature and pressure of the upstream and downstream cavities and the rotor speed. The steady state parameters that affect the flow also affect the dynamic response characteristics of the seal. Jet engine experiences have many cases in which knife-edge seal failures were due to high cycle fatigue (HCF). The sources of the dynamic excitations are attributed to one or more of the following: mechanical response due to flow path drivers or rotor dynamics; acoustic resonances that match the structural frequencies and mode shapes; and aero-elastic instability or flutter in which the mechanical deflections of the seal causes unsteady pressure loads that add work to the seal cycle over cycle with insufficient dissipation leading to large amplitude destructive vibratory stresses.